1. Field of the Invention
The present invention relates to a battery pack which measures a remaining battery charge.
2. Description of the Related Art
Recently, lithium-ion batteries have been loaded in mobile devices, for example, a digital still camera. In the lithium-ion battery, generally, it may be difficult to detect a remaining battery charge by its voltage. In order to detect the remaining battery charge of the battery, there is a method in which charging and discharging currents in the battery are accumulated (refer to Patent Document 1).
Since a current is consumed even if the lithium-ion battery is detached from the mobile device, a user needs a detector that detects the remaining battery charge by accumulating the charging and discharging currents of the lithium-ion battery, a regulator/protection circuit, and so on which are contained in a case as a battery pack.
In the detector, analog signals such as current values are converted into PCM (pulse code modulation) data which are digital values formed of multi bits, and the PCM data are accumulated. Consequently, an analog-to-digital converter is required to convert detected charging and discharging currents of the lithium-ion battery into the PCM data (refer to Patent Documents 2 and 3).
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-174534
[Patent Document 2] Japanese Laid-Open Patent Application No. 2001-102925
[Patent Document 3] Japanese Laid-Open Patent Application No. 2003-204267
Recently, the battery pack has been required to be small sized corresponding to the miniaturization of the mobile device. However, the circuit size of an analog-to-digital converter is large; therefore, it is difficult to install the detector in a small sized battery pack.